tailieunhanh - Chapter 128. Pneumococcal Infections

Streptococcus pneumoniae (the pneumococcus) was recognized as a major cause of pneumonia in the 1880s. Although the name Diplococcus pneumoniae was originally assigned to the pneumococcus, the organism was renamed Streptococcus pneumoniae because, like other streptococci, it grows in chains in liquid medium. Widespread vaccination has reduced the incidence of pneumococcal infection, but this organism remains the principal bacterial cause of otitis media, acute purulent rhinosinusitis, pneumonia, and meningitis. Microbiology Pneumococci are identified in the clinical laboratory as catalase-negative, gram-positive cocci that grow in pairs or chains and cause α-hemolysis on blood agar. More than 98% of pneumococcal isolates. | Chapter 128. Pneumococcal Infections Streptococcus pneumoniae the pneumococcus was recognized as a major cause of pneumonia in the 1880s. Although the name Diplococcus pneumoniae was originally assigned to the pneumococcus the organism was renamed Streptococcus pneumoniae because like other streptococci it grows in chains in liquid medium. Widespread vaccination has reduced the incidence of pneumococcal infection but this organism remains the principal bacterial cause of otitis media acute purulent rhinosinusitis pneumonia and meningitis. Microbiology Pneumococci are identified in the clinical laboratory as catalase-negative gram-positive cocci that grow in pairs or chains and cause a-hemolysis on blood agar. More than 98 of pneumococcal isolates are susceptible to ethylhydrocupreine optochin and virtually all pneumococcal colonies are dissolved by bile salts. Peptidoglycan and teichoic acid are the principal constituents of the pneumococcal cell wall whose integrity depends on the presence of numerous peptide side chains cross-linked by the activity of enzymes such as trans- and carboxypeptidases. P-Lactam antibiotics inactivate these enzymes by covalently binding their active site. Unique to S. pneumoniae and present in all strains is C-substance quot cell-wall quot substance a polysaccharide consisting of teichoic acid with a phosphorylcholine residue. Surface-exposed choline residues serve as a site of attachment for potential virulence factors such as pneumococcal surface protein A PspA and pneumococcal surface adhesin A PsaA which may prevent phagocytosis. Except for strains that cause conjunctivitis nearly every clinical isolate of S. pneumoniae has a polysaccharide capsule a structure that renders the bacteria virulent by preventing phagocytosis. All strains produce pneumolysin a toxin that may cause many of the manifestations of pneumococcal infection. There are 90 serologically distinct capsules of S. pneumoniae. Serotyping remains clinically relevant .

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